Valve operating apparatus for internal combustion engine

ABSTRACT

A valve operating apparatus includes: a first intermediate arm and a first rocker arm that are interposed between a first cam unit and a first valve; a second intermediate arm and a second rocker arm that are interposed between a second cam unit and a second valve; and hydraulic lash adjusters that rockably support the rocker arms. The intermediate arms are rockably supported by a rocker shaft. In the axial direction of the rocker shaft, the distance between the first transmission part and a bearing nearest thereto is shorter than the distance between the first pressure receiving part and a bearing nearest thereto, and likewise, the distance between the second transmission part and a bearing nearest thereto is shorter than the distance between the second pressure receiving part and a bearing nearest thereto.

BACKGROUND

Technical Field

Embodiments of the present disclosure relate to a valve operatingapparatus for an internal combustion engine.

Background Art

For example, JP 2001-263015 A discloses a variable valve operatingapparatus for an internal combustion engine. The variable valveoperating apparatus is an apparatus that can continuously change thelift amount and the operating angle of a valve (an intake valve or anexhaust valve).

More specifically, the variable valve operating apparatus includes anintermediate drive mechanism in a transmission path for the pressingforce which is transmitted from a cam to valves. The intermediate drivemechanism includes an input part and rocking cams which are rockablysupported by a support pipe that is disposed in parallel with acamshaft. The rocking cams are provided for the respective two valvesincluded in the same cylinder. The input part and the rocking cams areconfigured to rock integrally. The input part receives a pressing forcefrom the cam, and the rocking cams transmit the pressing force from thecam to the valves via rocker arms.

Further, the above described variable valve operating apparatus includesan actuator that displaces, in an axial direction of a control shaft,the control shaft which is disposed in the support pipe. Theintermediate drive mechanism is configured to be able to change arelative phase difference of the input part and the rocking cams inaccordance with a position in the axial direction of the control shaft.According to the variable valve operating apparatus having the aboveconfiguration, the relative phase difference of the input part and therocking cams is changed by adjusting the position in the axial directionof the control shaft, and as a result, the lift amount and the operatingangle of each of the valves can be changed.

JP 2010-019126 A and JP 2003-201814 A also show the state of the art atthe date of filing of this application.

Technical Problem

The variable valve operating apparatus disclosed in JP 2001-263015 A isconfigured to transmit the pressing force of a single cam to two valvesvia the input part and the two rocking cams of the intermediate drivemechanism. Meanwhile, a valve operating apparatus for an internalcombustion engine is known, in which a cam unit, an intermediate arm (amember interposed between the cam unit and a valve) that is rockablysupported by a rocker shaft, a rocker arm that is interposed between theintermediate arm and the valve, and a hydraulic lash adjuster thatoperates to eliminate a gap between the valve and the rocker arm and agap between the rocker arm and the intermediate arm are includedindependently for each valve. Here, in the intermediate arm, a partwhich is pressed by the cam unit is referred to as a “pressure receivingpart”, and a part which transmits the pressing force of the cam unit toa valve side (that is, the rocker arm) is referred to as a “transmissionpart”.

In the valve operating apparatus, it sometimes becomes necessary tooffset the position of the transmission part in the axial direction ofthe locker shaft with respect to the position of the pressure receivingpart in the same direction, for a reason, such as a constraint on thelayout of the cam unit. When such an offset is provided, the positionwhere the locker shaft receives a load from the cam side, and theposition where the rocker shaft receives a load from the valve sidediffer in the axial direction. When these loads become large, adeflection occurs to the rocker shaft at a time of valve opening. Whenthe offset is provided, if the positional relation of the pressurereceiving part and the transmission part in the axial direction of therocker shaft is not proper, the displacement amount of the transmissionpart (more specifically, a contact position with the rocker arm in thetransmission part) becomes large when a deflection occurs to the rockershaft.

When a deflection of the rocker shaft which supports the intermediatearm occurs at a time of valve opening, a very small gap sometimes isproduced between the intermediate arm and the rocker arm. The hydrauliclash adjuster acts to eliminate the gap instantly. At a time of valveclosing, the load to the intermediate arm from the rocker arm becomessmall, and therefore, the deflection of the rocker shaft is eliminatedor becomes small. However, even when the deflection of the rocker shaftbecomes small, it takes time until oil drains out of the hydraulic lashadjuster. Consequently, if the positional relation between the pressurereceiving part and the transmission part in the axial direction of therocker shaft is not appropriate, a closing failure of the valve mayoccur.

SUMMARY OF THE INVENTION

Embodiments of the present disclosure address the above-describedproblem and have an object to provide a valve operating apparatus for aninternal combustion engine that can improve a closing failure of a valvedue to the displacement of a transmission part accompanying thedeflection of a rocker shaft, in the internal combustion engine thatincludes a cam unit and an intermediate arm for each valve, and adopts aconfiguration in which the position of the transmission part in theaxial direction of the rocker shaft is offset to the position of apressure receiving part in the same direction.

A valve operating apparatus for an internal combustion engine accordingto the present disclosure includes: a first cam unit and a second camunit configured to respectively drive a first valve and a second valvethat are installed in a cylinder; a first intermediate arm interposedbetween the first cam unit and the first valve, and including a firstpressure receiving part that is pressed by the first cam unit and afirst transmission part that transmits a pressing force of the first camunit to a side of the first valve; a second intermediate arm interposedbetween the second cam unit and the second valve, and including a secondpressure receiving part that is pressed by the second cam unit and asecond transmission part that transmits a pressing force of the secondcam unit to a side of the second valve; a rocker shaft configured tosupport the first intermediate arm and the second intermediate arm to berockable between bearings that are respectively installed at both sidesof the cylinder; a first rocker arm interposed between the firstintermediate arm and the first valve, and configured to transmit apressing force from the first transmission part to the first valve; asecond rocker arm interposed between the second intermediate arm and thesecond valve, and configured to transmit a pressing force from thesecond transmission part to the second valve; a first hydraulic lashadjuster configured to rockably support the first rocker arm, and act toeliminate a gap between the first valve and the first rocker arm, and agap between the first rocker arm and the first intermediate arm; and asecond hydraulic lash adjuster configured to rockably support the secondrocker arm, and act to eliminate a gap between the second valve and thesecond rocker arm, and a gap between the second rocker arm and thesecond intermediate arm. In an axial direction of the rocker shaft, adistance between the first transmission part and the bearing that isnearest to the first transmission part is shorter than a distancebetween the first pressure receiving part and the bearing that isnearest to the first pressure receiving part, and a distance between thesecond transmission part and the bearing that is nearest to the secondtransmission part is shorter than a distance between the second pressurereceiving part and the bearing that is nearest to the second pressurereceiving part.

The first pressure receiving part and the second pressure receivingpart, and the first transmission part and the second transmission partmay be disposed on a same side with respect to the rocker shaft, seenfrom an axial direction of the cylinder.

The first cam unit may be configured by a first cam group including aplurality of cams having different profiles. The valve operatingapparatus may further include a device that switches a cam that gives apressing force to the first intermediate arm among the cams of the firstcam group.

The second cam unit may be configured by a second cam group furtherincludes a plurality of cams having different profiles. The valveoperating apparatus may further include a device that switches a camthat gives a pressing force to the second intermediate arm among thecams of the second cam group.

According to the valve operating apparatus for an internal combustionengine of the present disclosure, in the configuration including a camunit and an intermediate arm for each of valves, the positions of therespective transmission parts in the axial direction of the rocker shaftare offset with respect to the positions of the respective pressurereceiving parts in the same direction, in the following form. That is,in the axial direction of the rocker shaft, the distance between thefirst transmission part and the bearing that is the nearest to the firsttransmission part is configured to be shorter than the distance betweenthe first pressure receiving part and the bearing that is the nearest tothe first pressure receiving part. Similarly, in the axial direction ofthe rocker shaft, the distance between the second transmission part andthe bearing that is the nearest to the second transmission part isconfigured to be shorter than the distance between the second pressurereceiving part and the bearing that is the nearest to the secondpressure receiving part. According to the offsets in the form like this,the transmission parts are nearer to the bearings which are the fixedends as compared with the pressure receiving parts, and therefore, thedisplacement amounts of the transmission parts at the time of thepressing forces of the cams acting on the intermediate arms can berestrained to be small. The gaps which should be adjusted by thehydraulic lash adjusters thereby become small, and therefore, a closingfailure of the valves can be improved, which is caused by the hydrauliclash adjusters pushing the rocker arms excessively when the pressingforces of the cams do not act on the intermediate arms (that is, at thetime of valve closing).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of the outline of a valve operating apparatus for aninternal combustion engine according to a first embodiment of thepresent disclosure, seen from the axial direction of a cylinder;

FIG. 2A and FIG. 2B are sectional views of the valve operating apparatuscut along a line A-A in FIG. 1;

FIG. 3 is a perspective view of a pair of intermediate arms;

FIG. 4A and FIG. 4B are views for explaining an example of a specificconfiguration of a cam switching device included by the valve operatingapparatus shown in FIG. 1;

FIG. 5A to FIG. 5C are views for explaining switch operations of a camunit which are performed by the cam switching device;

FIG. 6A and FIG. 6B are views which relate to the first embodiment ofthe present disclosure, and are for explaining a difference of influenceof deflection of a rocker shaft due to a difference in the form ofoffsets;

FIG. 7 is a view of a main part of a valve operating apparatus for aninternal combustion engine according to a second embodiment of thepresent disclosure, seen from the axial direction of a cylinder, andshows a configuration included by each of the cylinders in the valveoperating apparatus;

FIG. 8 is a view of cam units, intermediate arms, rocker arms, hydrauliclash adjusters and valves seen from the axial direction of a rockershaft; and

FIG. 9A and FIG. 9B are views that relate to the second embodiment ofthe present disclosure, and are for explaining a difference in influenceof deflection of the rocker shaft due to difference in the manner ofoffsets.

DETAILED DESCRIPTION First Embodiment Configuration of Valve OperatingApparatus According to First Embodiment (Entire Configuration)

FIG. 1 is a view of the outline of a valve operating apparatus 10 for aninternal combustion engine according to a first embodiment of thepresent disclosure, seen from the axial direction of a cylinder. FIG. 2Aand FIG. 2B are sectional views of the valve operating apparatus 10 cutalong a line A-A in FIG. 1. More specifically, FIG. 2A is a view at atime of a first valve 12 a being in a valve closed state. FIG. 2B is aview at a time of the first valve 12 a being in a valve open state. FIG.3 is a perspective view of a pair of intermediate arms 20 (20 a, 20 b).

Each cylinder of the internal combustion engine is equipped with twointake valves and two exhaust valves. The valve operating apparatus 10is an apparatus for driving two valves (the two intake valves or the twoexhaust valves) 12 which are disposed in each cylinder of the internalcombustion engine. When the two valves 12 need to be distinguished fromeach other, the two valves are referred to as a first valve 12 a and asecond valve 12 b (this similarly applies to the components other thanthe valves 12). For the valve operating apparatus 10, FIG. 1 shows aconfiguration which is equipped for each of the cylinders.

The valve operating apparatus 10 includes a camshaft 14. The camshaft 14is connected to a crankshaft (not illustrated) via a timing pulley and atiming chain (or a timing belt) which are not illustrated, and isconfigured to rotate at a half of the speed of the crankshaft by therotational force of the crankshaft.

As shown in FIG. 1, a first cam unit 16 a and a second cam unit 16 b foreach cylinder are attached to the camshaft 14. The first cam unit 16 adrives the first valve 12 a via a first intermediate arm 20 a and afirst rocker arm 22 a which will be described later. The second cam unit16 b drives the second valve 12 b via a second intermediate arm 20 b anda second rocker arm 22 b which will be described later. In the presentembodiment, as an example, the first cam unit 16 a is configured by afirst cam group including three cams 16 a 1, 16 a 2 and 16 a 3, and thesecond cam unit 16 b is configured by a second cam group including threecams 16 b 1, 16 b 2 and 16 b 3. A configuration around the camshaft 14will be described later with reference to FIGS. 4A and 4B and FIGS. 5Ato 5C. Furthermore, as described below, the valve operating apparatus 10includes a rocker shaft 18, an intermediate arm 20, a rocker arm 22 anda cam switching device 24 (see FIG. 4A) as main components.

As shown in FIG. 1, the rocker shaft 18 is disposed in parallel with thecamshaft 14. The rocker shaft 18 is supported by a plurality of bearings26. More specifically, each of the bearings 26 is configured by abearing part which is formed at a cylinder head (or a cam carrier whichis attached to the cylinder head), and a cam cap (a camshaft supportmember) which is combined with the bearing part, and only the cam capsare illustrated in FIG. 1. A journal of the rocker shaft 18 is supportedby the bearing part and the cam cap. In order to allow the intermediatearm 20 to rock freely, a clearance for forming an oil film is providedbetween the journal, and the bearing part and the cam cap.

As shown in FIG. 1, the bearings 26 are respectively installed at bothsides of the cylinder. The first intermediate arm 20 a and the secondintermediate arm 20 b for the same cylinder are rockably supported bythe rocker shaft 18 between a pair of bearings 26 which are installed inthis way. As long as the intermediate arms 20 a and 20 b for the samecylinder are disposed between the pair of bearings 26, the two bearings26 do not have to be always included on a cylinder to cylinder basis.That is, one or both of the pair of bearings 26 may be shared byadjacent cylinders.

The first intermediate arm 20 a is interposed between the first cam unit16 a and the first valve 12 a. More specifically, since the first rockerarm 22 a is interposed between the first intermediate arm 20 a and thefirst valve 12 a, the first intermediate arm 20 a is interposed betweenthe first cam unit 16 a and the first rocker arm 22 a. In the firstintermediate arm 20 a, a first cam roller 28 a is rotatably attached toa position facing the first cam unit 16 a (more specifically, at aposition facing the first cam 16 a 2 in an operation state shown in FIG.1 and FIGS. 2A and 2B). The first cam roller 28 a corresponds to a“first pressure receiving part” which is pressed by the first cam unit16 a (to be more specific, 16 a 1 or 16 a 2).

Further, in the first intermediate arm 20 a, a first transmission part32 a is provided at a position facing a rocker roller 30 of the firstrocker arm 22 a. The first transmission part 32 a is a part thattransmits the pressing force of the first cam unit 16 a to the firstvalve 12 a via the first rocker arm 22 a. The first transmission part 32a is formed as a non-working surface 32 a 1 and a working surface 32 a2. The non-working surface 32 a 1 is a surface (a base circle part) in acircular-arc shape which is formed so that the distance from the centerof rocking (that is, the axial center of the rocker shaft 18) of thefirst intermediate arm 20 a is constant. The working surface 32 a 2 is asurface which is provided so as to continue from the non-working surface32 a 1, and is formed so that the distance from the center of rocking(the axis of the rocker shaft 18) of the first intermediate arm 20 abecomes gradually longer as the working surface 32 a 2 is away from thenon-working surface 32 a 1.

The second intermediate arm 20 b which is interposed between the secondcam unit 16 b and the second valve 12 b is configured similarly to theaforementioned first intermediate arm 20 a, except that a point whichwill be described in detail later (that is, a positional relationbetween the pressure receiving part and the transmission part) isdifferent. That is, the second intermediate arm 20 b includes a secondcam roller 28 b corresponding to the “second pressure receiving part”which is pressed by the second cam unit 16 b. Further, the secondintermediate arm 20 b is provided with a second transmission part 32 bwhich transmits a pressing force of the second cam unit 16 b to thesecond valve 12 b via the second rocker arm 22 b. The secondtransmission part 32 b is formed as a non-working surface 32 b 1 and aworking surface 32 b 2, similarly to the first transmission part 32 a.

As above, the valve operating apparatus 10 of the present embodimentincludes the cam unit 16 and the intermediate arm 20 independently foreach valve 12. Further, in order to be able to keep contact of the camunit 16 and the cam roller 28 at all times during rotational operationof the cam unit 16, the intermediate arm 20 is urged to the cam unit 16by a spring 34 (see FIG. 2A and FIG. 2B). An end part which is locatedat an opposite side of an end part at the intermediate arm 20 side inthe spring 34 is provided at the cylinder head or the cam carrier notillustrated.

Further, one end of the rocker arm 22 is supported by a valve shaft endof the valve 12, and the other end is supported by a hydraulic lashadjuster 36 (see FIG. 2A and FIG. 2B). More specifically, the valveoperating apparatus 10 includes a first hydraulic lash adjuster 36 a forthe first valve 12 a, and a second hydraulic lash adjuster 36 b for thesecond valve 12 b. The first hydraulic lash adjuster 36 a rockablysupports the first rocker arm 22 a, and acts to eliminate a gap betweenthe first valve 12 a and the first rocker arm 22 a and a gap between thefirst rocker arm 22 a and the first intermediate arm 20 a. The secondhydraulic lash adjuster 36 b rockably supports the second rocker arm 22b, and acts to eliminate a gap between the second valve 12 b and thesecond rocker arm 22 b and a gap between the second rocker arm 22 b andthe second intermediate arm 20 b. Further, the valve 12 is urged, by avalve spring 38 (see FIG. 2A and FIG. 2B), in a closing direction, thatis, a direction to push up the rocker arm 22.

Next, an opening and closing action of the valve 12 will be describedwith the second valve 12 b taken as an example. As shown in FIG. 2A, ina state where a pressing force of the second cam 16 b 2 is not given tothe second intermediate arm 20 b, the non-working surface 32 b 1 of thesecond transmission part 32 b abuts on the rocker roller 30 of thesecond rocker arm 22 b. In this state, the second rocker arm 22 b is notpressed down by the second intermediate arm 20 b, and therefore, thesecond valve 12 b keeps a valve closed state.

Meanwhile, when a pressing force of the second cam 16 b 2 is given tothe second intermediate arm 20 b, the second intermediate arm 20 b rockswith the rocker shaft 18 as a center as shown in FIG. 2B, and the partof the second transmission part 32 b which contacts the rocker roller 30is switched from the non-working surface 32 b 1 to the working surface32 b 2. As a result, the second rocker arm 22 b is pressed down by thesecond intermediate arm 20 b, and the second valve 12 b lifts. In thisway, the second cam 16 b 2 rotates, the second intermediate arm 20 bthereby rocks, and with this, the second rocker arm 22 b rocks, wherebythe second valve 12 b opens and closes.

(Cam Switching Device)

FIG. 4A and FIG. 4B are views for explaining an example of a specificconfiguration of the cam switching device 24 included by the valveoperating apparatus 10 shown in FIG. 1. More specifically, FIG. 4A is aview showing a configuration around the cam switching device 24 providedfor each of the cylinders of the internal combustion engine. FIG. 4B isa view of a cam unit 40 seen from the direction of an arrow B (the axialdirection of the camshaft 14) shown in FIG. 4A.

The first cam unit 16 a and the second cam unit 16 b described above areprovided as components of the cam unit 40. The cam unit 40 is supportedby the camshaft 14 in a form in which the cam unit 40 is movable in theaxial direction of the camshaft 14 and movement in the rotationaldirection thereof is restricted.

The cam switching device 24 switches the cam which is to be mechanicallyconnected to each of the valves 12 (that is, gives the pressing force tothe cam roller 28 of the intermediate arm 20) among the three cams (16 a1 to 16 a 3, or 16 b 1 to 16 b 3) having different profiles. The camswitching device 24 may include a configuration other than theconfiguration which will be described below as long as the cam switchingdevice is a device that can switch a plurality of cams which the camunit 16 has.

Here, an example of profiles of the three cams 16 a 1, 16 a 2 and 16 a 3of the first cam group will be described. The following explanationsimilarly applies to profiles of the three cams 16 b 1, 16 b 2 and 16 b3 of the second cam group. The profile of the cam 16 a 2 which isdisposed in the center of the first cam group (16 a 1, 16 a 2 and 16 a3) is set as a large cam for obtaining a relatively large lift amountand operating angle as a lift amount and an operating angle of the firstvalve 12 a. The cam 16 a 1 is disposed adjacently (the right side of thecam 16 a 2 in FIG. 4A) to the cam 16 a 2. The profile of the cam 16 a 1is set as a small cam which obtains a smaller lift amount and operatingangle than the lift amount and the operating angle obtained by the cam16 a 2. The cam 16 a 3 is disposed adjacently to the cam 16 a 2 (theleft side of the cam 16 a 2 in FIG. 4A) at an opposite side of the cam16 a 1. The profile of the cam 16 a 3 is set as a cam that only includesa base circle part in which the distance from the axis of the camshaft14 is equal, that is, a zero lift cam which does not give a pressingforce to the first valve 12 a.

Further, the cam unit 40 includes a guide groove 42. Although a locationof the guide groove 42 on the cam unit 40 is not specially limited, andin the present embodiment the guide groove 42 is formed on an outerperipheral surface of the cam unit 40, next to (at the left side of thesecond cam 16 b 3 in FIG. 4A) the second cam 16 b 3. The guide groove 42is formed to extend in a Y-shape in the circumferential direction. Morespecifically, the guide groove 42 has a pair of branch parts 42 a and 42b which is branched into a Y-shape, and a junction part 42 c which is alocation where the pair of branch parts 42 a and 42 b join each other.

At a position facing the guide groove 42, an electromagnetic solenoidtype actuator 44 having three cylindrical movable elements 44 a, 44 band 44 c capable of engaging with and disengaging from the guide groove42 is disposed. The actuator 44 is electrically connected to anelectronic control unit (ECU) 46 for controlling the internal combustionengine including the valve operating apparatus 10. Energization of theactuator 44 is controlled on the basis of an instruction from the ECU46. The actuator 44 is configured to be able to push out a movableelement of the three movable elements 44 a, 44 b and 44 c toward theguide groove 42 in a state where electric power is turned on.

More specifically, each of the movable elements 44 a, 44 b and 44 c isurged, by a spring not illustrated, in a direction to separate from theguide groove 42. The actuator 44 is configured so that the thrust forceof a solenoid which is generated as a result of energization surpassesthe force of the spring, and thereby the movable element 44 a, 44 b or44 c can protrude (advance) to the guide groove 42. Further, theactuator 44 is attached to the cylinder head or the cam carrier notillustrated. The cam switching device 24 is equipped with a stopperdevice (not illustrated) between the cam unit 40 and the camshaft 14, inorder to keep an axial position of the cam unit 40 on the camshaft 14,in a state where none of the movable elements 44 a, 44 b and 44 c isengaged with the guide groove 42.

Further, as shown in FIG. 4A, the distance between groove center linesof the first branch part 42 a and the junction part 42 c in the guidegroove 42, and the distance between groove center lines of the secondbranch part 42 b and the junction part 42 c are configured to be equalto the distance between cam center lines in the width direction of theadjacent cams in the cam unit 16. Further, each of distances betweencenter lines of the respective movable elements 44 a, 44 b and 44 c ofthe actuator 44 is configured to be equal to the above describeddistance between the groove center lines.

FIG. 5A to FIG. 5C are views for explaining switch operations of the camunit 16 which are performed by the cam switching device 24. FIG. 5Ashows an operation state (state using the large cams) where the cam 16 a2 of the first cam group and the cam 16 b 2 of the second cam grouprespectively contact the first cam roller 28 a and the second cam roller28 b, similarly to FIG. 4A. The cam switching device 24 is configured sothat in this operation state, the groove center line of the first branchpart 42 a coincides with the center line of the first movable element 44a, and the groove center line of the second branch part 42 b coincideswith the center line of the third movable element 44 c.

When the actuator 44 is operated so that the first movable element 44 ais inserted into the first branch part 42 a during use of a common basecircle part concerning the first cam unit 16 a and the second cam unit16 b in the operation state shown in FIG. 5A, the guide groove 42 slidesthe cam unit 40 in a direction shown in FIG. 5B by using a rotationalforce of the camshaft 14. As a result, the cams respectively contactingthe cam rollers 28 a and 28 b are switched to the cams 16 a 3 and 16 b 3from the cams 16 a 2 and 16 b 2 as a result of rotation of the camshaft14. In this way, with the operation of the actuator 44, the operationstate of the cam switching device 24 is switched to an operation stateshown in FIG. 5B (a valve stopped state). When a state where theposition of the first movable element 44 a coincides with the positionof the junction part 42 c in the axial direction of the camshaft 14 isbrought about as a result of the aforementioned slide operation,energization of the actuator 44 is stopped quickly. As a result, thefirst movable element 44 a is removed from the guide groove 42. Inaddition, the axial position of the cam unit 40 is kept by theaforementioned stopper device. This similarly applies to switch of otheroperation states which will be described below.

In the operation state shown in FIG. 5B, the groove center line of thesecond branch part 42 b of the guide groove 42 coincides with the centerline of the second movable element 44 b. When the actuator 44 operatesin this operation state so that the second movable element 44 b isinserted into the second branch part 42 b during use of the common basecircle part concerning the first cam unit 16 a and the second cam unit16 b, the guide groove 42 switches, by using the rotational force of thecamshaft 14, the cams which respectively contact the cam rollers 28 aand 28 b to the cams 16 a 2 and 16 b 2 from the cams 16 a 3 and 16 b 3as a result of rotation of the camshaft 14. The operation state of thecam switching device 24 is thereby switched (is returned) to theoperation state shown in FIG. 5A again as a result of the operation ofthe actuator 44.

Meanwhile, when the actuator 44 operates in the operation state shown inFIG. 5A so that the third movable element 44 c is inserted into thesecond branch part 42 b during use of the common base circle partconcerning the first cam unit 16 a and the second cam unit 16 b, theguide groove 42 slides the cam unit 40 in a direction shown in FIG. 5Cby using the rotational force of the camshaft 14. As a result, the camswhich respectively contact the cam rollers 28 a and 28 b are switched tothe cams 16 a 1 and 16 b 1 from the cams 16 a 2 and 16 b 2 as a resultof rotation of the camshaft 14. The operation state of the cam switchingdevice 24 is thereby switched to the operation state (a state usingsmall cams) shown in FIG. 5C as a result of the operation of theactuator 44.

In the operation state shown in FIG. 5C, the groove center line of thefirst branch part 42 a of the guide groove 42 coincides with the centerline of the second movable element 44 b. When the actuator 44 operatesin this operation state so that the second movable element 44 b isinserted into the first branch part 42 a during use of the common basecircle part concerning the first cam unit 16 a and the second cam unit16 b, the guide groove 42 switches, by using the rotational force of thecamshaft 14, the cams which respectively contact the cam rollers 28 aand 28 b to the cams 16 a 2 and 16 b 2 from the cams 16 a 1 and 16 b 1as a result of rotation of the camshaft 14. The operation state of thecam switching device 24 is thereby switched (is returned) to theoperation state shown in FIG. 5A again as a result of the operation ofthe actuator 44.

The above described cam switching device 24 is configured by theaforementioned components (that is, the cam unit 40 which is attached tothe camshaft 14 in a form that the cam unit 40 is movable in the axialdirection of the camshaft 14 and the movement thereof is restricted inthe rotational direction, the guide groove 42 and the actuator 44).

As described above, according to the valve operating apparatus 10 of thepresent embodiment, the lift amounts and the operating angles of thevalves 12 can be changed stepwise, which includes realization of thevalve stopped state where the valves 12 are kept in a closed state, byswitching, with the cam switching device 24, the cams which give thepressing forces to the cam rollers 28 of the intermediate arms 20 amongthe plurality of cams which the cam units 16 have. In this way, thevalve operating apparatus 10 of the present embodiment is configured asa variable valve operating apparatus capable of changing the valveopening characteristics of the valves 12. In the configuration so far,the cams 16 a 3 and 16 b 3 are both zero lift cams, but the presentdisclosure is not limited to this. If only either one of the cam 16 a 3and the cam 16 b 3 is, for example, a zero lift cam, an operation ofstopping only one of the valves 12 can be implemented.

Characteristic Configuration of Valve Operating Apparatus According toFirst Embodiment and Effect by the Configuration

The valve operating apparatus which is mounted in an internal combustionengine is requested to be established in a limited mounting space in thecylinder head. For the configuration of the intermediate arms 20, thevalve operating apparatus 10 of the present embodiment has a featurethat will be described as follows. As a result, in the configuration inwhich each of the valves 12 includes the cam unit 16 and theintermediate arm 20 which is rockably supported by the rocker shaft 18,occurrence of a negative effect which is caused by displacement of thetransmission part accompanying deflection of the rocker shaft 18 can berestrained while a space necessary to mount the valve operatingapparatus 10 is reduced to be small, as described in detail below.

(Saving Space in Height Direction of Cylinder Head)

According to the valve operating apparatus 10 of the present embodimentdescribed above, the intermediate arms 20 are configured so that thefirst cam roller 28 a (the first pressure receiving part) and the secondcam roller 28 b (the second pressure receiving part), and the firsttransmission part 32 a and the second transmission part 32 b are locatedon the same side with respect to the rocker shaft 18, seen from theaxial direction of the cylinder (see FIG. 1). Hereinafter, thedisposition like this will be referred to as a “disposition A” forconvenience. To add to that, in the intermediate arms 20, the positionof the first transmission part 32 a in the axial direction of the rockershaft 18 is offset with respect to the position of the first cam roller28 a (the first pressure receiving part), and the position of the secondtransmission part 32 b in the axial direction of the rocker shaft 18 issimilarly offset with respect to the position of the second cam roller28 b (the second pressure receiving part). If the above describedoffsets are adopted in an example where the above described dispositionA is adopted, the mounting position of the camshaft can be restrained tobe low as compared with an example without offsets. As a result, theheight of the cylinder head can be restrained to be low. In other words,a space in the height direction of the cylinder head (that is, the axialdirection of the cylinder) shown in FIG. 3 can be saved.

(Restraint on Displacement of Transmission Part Due to Deflection ofRocker Shaft)

In addition, the above described offsets in the intermediate arms 20 areset with the following form (hereinafter, referred to as a “form A” forconvenience of explanation). That is, according to the form A mentionedhere, in the axial direction of the rocker shaft 18, the distancebetween the first transmission part 32 a and the bearing 26 (the bearing26 at the right side in FIG. 1) which is the nearest to the firsttransmission part 32 a is set to be shorter than the distance betweenthe first cam roller 28 a (the first pressure receiving part) and thebearing 26 (the same bearing 26 at the right side in FIG. 1) which isthe nearest to the first cam roller 28 a. Further, according to the formA, in the axial direction of the rocker shaft 18, the distance betweenthe second transmission part 32 b and the bearing 26 (the bearing 26 atthe left side in FIG. 1) which is the nearest to the second transmissionpart 32 b is set to be shorter than the distance between the second camroller 28 b and the bearing 26 (the same bearing 26 at the left side inFIG. 1) which is the nearest to the second cam roller 28 b (the secondpressure receiving part). An effect obtained by providing the offsets inthe form A like this will be described below with reference to FIG. 6Aand FIG. 6B.

FIG. 6A and FIG. 6B are views which relate to the first embodiment ofthe present disclosure, and are for explaining a difference of influenceof deflection of the rocker shaft due to a difference in the form ofoffsets. More specifically, FIG. 6A is a view of an example whereoffsets in the form A which is adopted in the present embodiment areprovided. FIG. 6B is a view showing a comparative example which isreferred to for the purpose of being compared with the configuration ofthe present embodiment. As a form that can be adopted as the abovedescribed offsets, there is a form that is adopted in the comparativeexample shown in FIG. 6B, other than the form A. That is, the offsetscan also be provided in this form in which the positions where loadsfrom the cams are received are nearer to the bearings as compared withthe positions where loads from the rocker arms (valve side) arereceived, contrary to the form A.

First, as shown in the respective views in FIG. 6A and FIG. 6B, if thepressing force of each cam is given to the intermediate arm, the loadfrom the cam acts on the pressure receiving part of the intermediatearm. In addition, if the pressing force is given, a load which is causedby a valve spring reaction force that is produced by receiving theaforementioned pressing force and the magnitude of which is equivalentto the load from the cam, acts on the transmission part of theintermediate arm from the valve side (acts via the rocker arm 22 in theexample of the valve operating apparatus 10). If the offsets areprovided, in the axial direction the position where the rocker shaftreceives the load from the cam side differs from the position where therocker shaft receives the load from the valve side, even though eitherform of the forms in FIG. 6A and FIG. 6B is adopted. As a result, adeflection occurs to the rocker shaft.

In the comparative example shown in FIG. 6B, at the position where theload from each rocker arm (each valve side) is received, the distancefrom the bearing which is nearer to the intermediate arm out of the pairof bearings is longer than that at the position where the load from thecam is received. Consequently, the moment which is produced with thebearing as the center and which is of the load from each rocker arm(each valve side) becomes larger than the moment of the load from eachcam. FIG. 6B shows a state where the rocker shaft deflects in a mannerwhere the rocker shaft is pushed toward the cam side (in the upwarddirection in FIG. 6B).

Meanwhile, the configuration of the present embodiment shown in FIG. 6Aadopts offsets in the opposite form (that is, form A) to the comparativeexample shown in FIG. 6B as described above. Consequently, concerningthe moment with, as the center, the bearing 26 nearer to theintermediate arm 20 to which attention is paid, the moment of the loadfrom each rocker arm 22 (each valve 12 side) is smaller than the momentof the load from each cam unit 16. FIG. 6A shows a state where therocker shaft deflects in a manner where the rocker shaft is pushedtoward the valve side (in the downward direction in FIG. 6A).

In the example where the form A is used, the position of eachtransmission part becomes nearer to the bearing (the bearing nearer tothe intermediate arm to which attention is paid) which is a fixed end,as compared with the example where the form in which the positionalrelation of the pressure receiving part and the transmission part areopposite to the form A is used. Consequently, as is understandable whenFIG. 6A and FIG. 6B are compared, when attention is paid to the positionof each transmission part in the axial direction of the rocker shaft,the deflection amount δ of the rocker shaft in the position of eachtransmission part becomes smaller in the configuration shown in FIG. 6A,as compared with the configuration shown in FIG. 6B. Accordingly, thedisplacement amount of each transmission part (more specifically, thedisplacement amount of each contact position with a mating member (inthe valve operating apparatus 10, the rocker roller 30 corresponds tothis) in each transmission part) at the time of the pressing force ofeach cam acting on the intermediate arm becomes smaller in theconfiguration shown in FIG. 6A, as compared with the configuration shownin FIG. 6B. A straight line L1 in each of FIG. 6A and FIG. 6B representsthe center axis of the rocker shaft at a time of no deflection occurringto the rocker shaft, and straight lines L2 and L2′ in FIG. 6A and FIG.6B represent center axes of the rocker shafts at a time of deflectionoccurring. This similarly applies to FIG. 9A and FIG. 9B which will bedescribed later.

When the rocker shaft which supports the intermediate arms deflects inthe upward direction in FIG. 6A at a time of opening of the valves, verysmall gaps are generated between the intermediate arms and the rockerarms. More specifically, gaps are generated between the rocker rollersof the rocker arms and the non-working surfaces (the base circle parts)of the intermediate arms. The hydraulic lash adjusters act to eliminatethe gaps instantly. Meanwhile, the loads to the intermediate arms fromthe rocker arms become small at a time of valve closing, and therefore,the deflection of the rocker shaft is eliminated or decreases. However,even though the deflection of the rocker shaft becomes small, it takestime until oil drains from the hydraulic lash adjusters. Consequently,when deflection decreases in the state where the positions of supportpoints of the rocker arms at the hydraulic lash adjuster side becomehigh as a result of the hydraulic lash adjusters acting to eliminate thegaps, there is a possibility that the valves may be pressed by therocker arms due to the fact that the positions of the support pointshave become high (that is, the fact that the gaps have been eliminated),even during a time period in which the pressing forces from the cams donot act on the intermediate arms. Consequently, if the displacementamounts of the transmission parts of the intermediate arms due todeflection of the rocker shaft are large, a closing failure of thevalves may occur.

However, according to the configuration of the intermediate arms 20 ofthe present embodiment, the displacement amounts of the transmissionparts 32 can be reduced when deflection occurs to the rocker shaft 18due to adoption of offsets. As a result, the closing failure of thevalves 12 due to the influence of the action of the aforementionedhydraulic lash adjusters 36 can be improved.

(Saving of Space in Axial Direction in Example of Having Configurationof Making Opening Characteristics of Valves Variable by Using SlideOperations of Cams)

The offsets in the form A of the present embodiment also provides thefollowing effect when the offsets in the form A are applied to a valveoperating apparatus having the configuration in which the openingcharacteristics of the valves are made variable by switching the camswhich press the valves by sliding a plurality of cams in the axialdirection of the camshaft as in the valve operating apparatus 10. Thatis, in the example of having the configuration in which a plurality ofcams are slid in the axial direction of the camshaft, a large space isrequired in the axial direction of the camshaft in order to establishthe slide operation. The issue becomes more remarkable as the number ofcams to be slid is larger.

For the above described issue, according to the offsets in the form A,in other words, the form in which the pressure receiving parts (that is,the cam rollers 28) are disposed at inner sides of the first valve 12 aand the second valve 12 b in the axial direction of the rocker shaft 18,a space between the first valve 12 a and the second valve 12 b in theaxial direction of the rocker shaft 18 can be more effectively used forthe slide operations of the cam units 16, as compared with the form inwhich the positional relation of the pressure receiving parts and thetransmission parts is opposite to that in the form A. The reason is thatthe first and second cam units 16 a and 16 b are disposed near to thecenter side of the cylinders, so that the variable device for changingthe opening characteristics of the valves 12 is easily disposed at outersides of the cylinder relative to the first and second cam units 16 aand 16 b. As a result, the space in the axial direction (the axialdirection shown in FIG. 3) of the camshaft 14 can be saved, andtherefore, the configuration which makes the opening characteristics ofthe valves variable can be easily established by using the slideoperation of the cams.

(Saving Space in Width Direction of Cylinder Head)

In the intermediate arms 20, the first cam roller 28 a (the firstpressure receiving part) and the second cam roller 28 b (the secondpressure receiving part), and the first transmission part 32 a and thesecond transmission part 32 b are disposed on the same side with respectto the rocker shaft 18 seen from the axial direction of the cylinder(see FIG. 1). According to the disposition A, even where the spaceensured to mount the valve operating apparatus is small for the reasonthat bore diameters of the cylinders are small, for example, the valveoperating apparatus can be easily established in the limited space. Morespecifically, the space can be saved in the width direction of thecylinder head shown in FIG. 3 (that is, a direction that is orthogonalto each of the axial direction of the cylinders and the axial directionof the camshaft 14).

Modified Example of First Embodiment

In the first embodiment described above, explanation is made by taking,as an example, the valve operating apparatus (that is, the variablevalve operating apparatus) 10 including, as the first cam unit 16 awhich drives the first valve 12 a, the first cam unit 16 a configured bythe first cam group formed of a plurality (three as an example) of thecams 16 a 1 to 16 a 3 having different profiles, and also including thesimilar configuration concerning the second cam unit 16 b. However, thefirst cam unit and the second cam unit included by the valve operatingapparatus of the internal combustion engine which is the object of thepresent disclosure may be each configured by a single cam. Morespecifically, the valve operating apparatus to be the object of thepresent disclosure may be, for example, configured as a valve operatingapparatus which does not have the function of making variable theopening characteristics of the valves by adopting, for each intermediatearm 20, the configuration which drives, via the intermediate arm 20 andthe rocker arm 22, a valve by a single fixed cam. Alternatively, thevalve operating apparatus to be the object of the present disclosure maybe configured as a variable valve operating apparatus having thefunction of making variable the opening characteristics of the valves byadopting, for each intermediate arm, a configuration that includes aknown variable device which makes the operation of the intermediate armsvariable while including, for each of the intermediate arms, theconfiguration that drives a valve by a single cam via the inter mediatearm and the rocker arm.

Further, in the first embodiment described above, explanation is made bytaking, as an example, the valve operating apparatus 10 including thefirst cam roller 28 a and the second cam roller 28 b respectively as thefirst pressure receiving part and the second pressure receiving part.However, the parts corresponding to the first pressure receiving partand the second pressure receiving part in the present disclosure are notlimited to the parts that contact the cams with rolling contact as inthe example of using the cam rollers 28, but may be parts using slidecontact similarly to a valve operating apparatus 50 which will bedescribed later. That is, the above described parts may be formed at theintermediate arms as pads having curved surfaces or flat surfaces whichcontact the cams. Further, the pressure receiving part in the presentdisclosure is not necessarily limited to the part that directly contactsthe cam itself as long as the part is pressed by the cam, and may beconfigured to be pressed by the cam via a member, for example.

Further, in the first embodiment described above, explanation is made bytaking, as an example, the valve operating apparatus 10 including thesingle cam-switching device 24 for each of the cylinders. However, thesingle cam-switching device in the present disclosure may be includedfor each of the valves. If the single cam-switching device is includedfor each of the valves, single valve control (for example, single valvestop control of bringing only one of the valves into a stopping state,for example) that causes the opening characteristic of one of the firstvalve and the second valve to differ from the opening characteristic ofthe other one can be performed. Alternatively, the device which switchesthe cam in the present disclosure may be shared among a plurality ofcylinders which share the base circle part of the cams.

Second Embodiment

Next, a second embodiment of the present disclosure will be describedwith reference to FIG. 7 to FIG. 9B.

Configuration of Valve Operating Apparatus According to SecondEmbodiment

In the first embodiment described above, explanation is made by taking,as an example, the valve operating apparatus 10, which adopts thedisposition A (that is, the disposition in which the first cam roller 28a (the first pressure receiving part) and the second cam roller 28 b(the second pressure receiving part), and the first transmission part 32a and the second transmission part 32 b are included on the same sidewith respect to the rocker shaft 18 seen from the axial direction of thecylinder). Here, in the valve operating apparatus for an internalcombustion engine, disposition as follows, that is, a disposition(hereinafter, referred to as a “disposition B” for convenience ofexplanation) is sometimes used in which a pressure receiving part isprovided at an opposite side of a transmission part with respect to arocker shaft, seen from the axial direction of a cylinder, other thanthe aforementioned disposition A. Even in the valve operating apparatusadopting the disposition B like this, it is sometimes necessary tooffset the positions of the transmission parts in the axial direction ofthe rocker shaft with respect to the positions of the pressure receivingparts in the same direction, for the reason, such as a constraint on thelayout of the cam units. The valve operating apparatus 50 of the presentembodiment which will be described below is preferable in restrainingoccurrence of the harmful effect due to displacement of the transmissionparts accompanying a deflection of the rocker shaft when the dispositionB is adopted.

FIG. 7 is a view of a main part of the valve operating apparatus 50 foran internal combustion engine according to the second embodiment of thepresent disclosure, seen from the axial direction of a cylinder, andshows a configuration included by each of the cylinders in the valveoperating apparatus 50. FIG. 8 is a view of cam units 56, intermediatearms 54, the rocker arms 22, the hydraulic lash adjusters 36 and thevalves 12 seen from the axial direction of a rocker shaft 58. In FIG. 7and FIG. 8, the same components as the components shown in FIG. 1described above will be assigned with the same reference signs andexplanation thereof will be omitted or simplified.

As shown in FIG. 7, for each cylinder, a first cam unit 56 a whichdrives the first valve 12 via a first intermediate arm 54 a and thefirst rocker arm 22 a, and a second cam unit 56 b which drives thesecond valve 12 b via a second intermediate arm 54 b and the secondrocker arm 22 b are attached to a camshaft 52. In the example of thevalve operating apparatus 50 of the present embodiment, the first camunit 56 a and the second cam unit 56 b are each configured by a singlecam. The first intermediate arm 54 a and the second intermediate arm 54b are rockably supported by the rocker shaft 58.

The first intermediate arm 54 a includes a first pressure receiving part60 a which is pressed by the first cam unit 56 a, and a firsttransmission part 62 a which transmits the pressing force of the firstcam unit 56 a to the first valve 12 a side (the first rocker arm 22 a).Similarly, the second intermediate arm 54 b includes a second pressurereceiving part 60 b which is pressed by the second cam unit 56 b, and asecond transmission part 62 b which transmits the pressing force of thesecond cam unit 56 b to the second valve 12 b side (the second rockerarm 22 b).

As shown in FIG. 7, the valve operating apparatus 50 adopts thedisposition B in which the pressure receiving parts 60 a and 60 b areprovided at the opposite side of the transmission parts 62 a and 62 bwith respect to the rocker shaft 58, seen from the axial direction ofthe cylinder. In addition to that, in the intermediate arms 54 of thepresent embodiment, offsets concerning the pressure receiving parts 60and the transmission parts 62 are set in a manner as follows(hereinafter, referred to as a “manner A′” for convenience ofexplanation). That is, in the manner A′ mentioned here, in the axialdirection of the rocker shaft 58, the distance between the firsttransmission part 62 a and the bearing 26 (the bearing 26 at the rightside in FIG. 7) which is the nearest to the first transmission part 62 ais set to be shorter than the distance between the first pressurereceiving part 60 a and the bearing 26 (the same bearing 26 at the rightside in FIG. 7) which is the nearest to the first pressure receivingpart 60 a. Further, in the manner A′, the distance between the secondtransmission part 62 b and the bearing 26 (the bearing 26 at a left sidein FIG. 7) which is the nearest to the second transmission part 62 b thesecond transmission part 62 b is set to be shorter than the distancebetween the second pressure receiving part 60 b and the bearing 26 (thesame bearing 26 at the left side in FIG. 7) which is the nearest to thesecond pressure receiving part 60 b. An effect by providing offsets inthe manner A′ like this will be described below with reference to FIG.9A and FIG. 9B.

FIG. 9A and FIG. 9B are views that relate to the second embodiment ofthe present disclosure, and are for explaining a difference in influenceof deflection of the rocker shaft due to difference in the manner ofoffsets. More specifically, FIG. 9A is a view of a configuration whereoffsets in the mariner A′ which is adopted in the present embodiment areprovided. FIG. 9B is a view showing a comparative example which isreferred to for the purpose of being compared with the configuration ofthe present embodiment.

First, when the disposition B is adopted, loads from the cams and loadsfrom the valves are both act onto the rocker shaft 58 in substantiallythe same direction as shown in FIG. 8, unlike the disposition Adescribed in the first embodiment. As a result, the rocker shaftdeflects in such a manner as to be pressed to the upward direction inFIG. 9A and FIG. 9B, in both configurations in FIG. 9A and FIG. 9B.

As described above, in the manner A′ of the present embodiment, thedistances between the transmission parts 62 a and 62 b and the bearings26 which are the nearest to them are set to be shorter than thedistances between the pressure receiving parts (cam rollers) 60 a and 60b and the bearings 26 which are the nearest to them. According to theconfiguration like this, the deflection amount δ of the rocker shaft ineach of the positions of the transmission parts becomes smaller as shownin FIG. 9A, as compared with the comparative example (FIG. 9B) whichadopts the configuration opposite from this. Accordingly, by the valveoperating apparatus 50 of the present embodiment which adopts theoffsets in the manner A′, the harmful effect (more specifically, aclosing failure of the valves 12) due to displacements of thetransmission parts 62 a and 62 b accompanying the deflection of therocker shaft 58 can also be restrained, similarly to the valve operatingapparatus 10 of the first embodiment.

What is claimed is:
 1. A valve operating apparatus for an internalcombustion engine, comprising: a first cam unit and a second cam unitconfigured to respectively drive a first valve and a second valve thatare installed in a cylinder; a first intermediate arm interposed betweenthe first cam unit and the first valve, and including a first pressurereceiving part that is pressed by the first cam unit and a firsttransmission part that transmits a pressing force of the first cam unitto a side of the first valve; a second intermediate arm interposedbetween the second cam unit and the second valve, and including a secondpressure receiving part that is pressed by the second cam unit and asecond transmission part that transmits a pressing force of the secondcam unit to a side of the second valve; a rocker shaft configured tosupport the first intermediate arm and the second intermediate arm to berockable between bearings that are respectively installed at both sidesof the cylinder; a first rocker arm interposed between the firstintermediate arm and the first valve, and configured to transmit apressing force from the first transmission part to the first valve; asecond rocker arm interposed between the second intermediate arm and thesecond valve, and configured to transmit a pressing force from thesecond transmission part to the second valve; a first hydraulic lashadjuster configured to rockably support the first rocker arm, and act toeliminate a gap between the first valve and the first rocker arm, and agap between the first rocker arm and the first intermediate arm; and asecond hydraulic lash adjuster configured to rockably support the secondrocker arm, and act to eliminate a gap between the second valve and thesecond rocker arm, and a gap between the second rocker arm and thesecond intermediate arm, wherein, in an axial direction of the rockershaft, a distance between the first transmission part and the bearingthat is nearest to the first transmission part is shorter than adistance between the first pressure receiving part and the bearing thatis nearest to the first pressure receiving part, and a distance betweenthe second transmission part and the bearing that is nearest to thesecond transmission part is shorter than a distance between the secondpressure receiving part and the bearing that is nearest to the secondpressure receiving part.
 2. The valve operating apparatus according toclaim 1, wherein the first pressure receiving part and the secondpressure receiving part, and the first transmission part and the secondtransmission part are disposed on a same side with respect to the rockershaft, seen from an axial direction of the cylinder.
 3. The valveoperating apparatus according to claim 1, wherein the first cam unit isconfigured by a first cam group including a plurality of cams havingdifferent profiles, and wherein the valve operating apparatus furthercomprises a device that switches a cam that gives a pressing force tothe first intermediate arm among the cams of the first cam group.
 4. Thevalve operating apparatus according to claim 1, wherein the second camunit is configured by a second cam group further includes a plurality ofcams having different profiles, and wherein the valve operatingapparatus further comprises a device that switches a cam that gives apressing force to the second intermediate arm among the cams of thesecond cam group.